Is the HD-SDI output always pre-codec?

[Roy Bemelmans]

Couple of questions regarding HD-SDI:

- Is the HD-SDI ouput signal on cameras always created straight from the CCD (so to speak, I'm no camera expert) giving you pristine quality or are there cameras that convert video that's already compressed using their codec (HDV, HDCAM) to HD-SDI giving you loads of unnecessary data?

- Also, do only HDV or DVCPRO-HD cameras allow realtime capturing of their compressed video via firewire?

- AIUI, high-end compressed formats like HDCAM (SR) or D5 or always transferred via HD-SDI. Wouldn't a tape deck deck need to recompress e.g. everytime it records from another deck via HD-SDI, resulting in quality loss?

Thanks

[David Newman]

1) HD-SDI or analog compoent output are pre-compression, although there is a lot of processing after the CCD before it is sent out. Thisis the data you want for the best chroma keys or simply the highest quality.

2) Yes.

3) Yes, these deck do recompress, yet for D5 and HDCAM SR the bit-rates are high-enough that this is not a major concern. It is more a concern with standard HDCAM and DVCPRO-HD which have lower bit-rate and also resample the image over HD-SDI, so be warned.

[Roy Bemelmans]

Originally Posted by David Newman

2) Yes.

So on a studio shoot, you could record HDV or DVCPRO-HD straight into your computer running your NLE/Cineform via firewire, right?

Originally Posted by David Newman

3) Yes, these decks do recompress, yet for D5 and HDCAM SR the bit-rates are high-enough that this is not a major concern. It is more a concern with standard HDCAM and DVCPRO-HD which have lower bit-rate and also resample the image over HD-SDI, so be warned.

So theoretically it's impossible to make a perfect digital copy of e.g. a D5 master..

There aren't any DVCAM (SR) cameras/decks that output compressed via firewire, are there? Wouldn't this solve the above problem?

[David Newman]

Originally Posted by Roy Bemelmans

So on a studio shoot, you could record HDV or DVCPRO-HD straight into your computer running your NLE/Cineform via firewire, right?

In a studio shoot it is best not to use the compression FireWire output and capture from the component's as pre-compression outputs. Maybe when I said "Yes" to you last question I wasn't clear on you question. Firewire is always the sub-sampled and compressed image.

There aren't any DVCAM (SR) cameras/decks that output compressed via firewire, are there? Wouldn't this solve the above problem?

Not via firewire, HDCAM to Sony Xpri is "native" over HSDL (I believe a protocol over HD-SDI) otherwise there is loss. Deck to deck dubs serve little function, generally you input raw footage and output enhanced footage, so HSDL will not help you.

[Roy Bemelmans]

Originally Posted by David Newman

In a studio shoot it is best not to use the compression FireWire output and capture from the component's as pre-compression outputs. Maybe when I said "Yes" to you last question I wasn't clear on you question. Firewire is always the sub-sampled and compressed image.

You were very clear, David. I was just wondering whether you can record HDV or DVCPRO-HD straight into your computer running your NLE/Cineform via firewire instead of using a dedicated direct-to-disk solution.. (a bit of a newbie question I guess)

[David Newman]

Oh, yes of course, HDV over FireWire that is what 99.5% of our customers are doing. Note: DVCPRO-HD is not currently support by Aspect HD, Premiere or Vegas, and no I can't say when it will either.

[Roy Bemelmans]

Thanks David. Since you're obviously quite knowledgeable please take a look at another thread I started here about SMPTE timecode in digital video and how NLEs handle this..